U.S. patent application number 15/512944 was filed with the patent office on 2017-10-26 for lc-based optical display system.
This patent application is currently assigned to Yissum Research Development Company Of The Hebrew University of Jerusalem Ltd.. The applicant listed for this patent is Merck Patent GmbH, QLight Nanotech Ltd., Yissum Research Development Company Of The Hebrew University of Jerusalem Ltd.. Invention is credited to Hagai ARBELL, Uri BANIN, Bernhard RIEGER, Ming-Chou WU.
Application Number | 20170307939 15/512944 |
Document ID | / |
Family ID | 54337845 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170307939 |
Kind Code |
A1 |
BANIN; Uri ; et al. |
October 26, 2017 |
LC-BASED OPTICAL DISPLAY SYSTEM
Abstract
An optically active structure and a display device are
presented. The device utilized an optically active structure
comprising liquid crystal material and a plurality of nanorods
configured to emit light in one or more predetermined ranges in
response to pumping light. Variation in orientation of the liquid
crystal varies orientation of the nanorods and modulated light
emission therefrom.
Inventors: |
BANIN; Uri; (Mevasseret
Zion, IL) ; ARBELL; Hagai; (Jerusalem, IL) ;
RIEGER; Bernhard; (Muenster, DE) ; WU; Ming-Chou;
(Zhongli City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yissum Research Development Company Of The Hebrew University of
Jerusalem Ltd.
QLight Nanotech Ltd.
Merck Patent GmbH |
Jerusalem
Jerusalem
Darmstadt |
|
IL
IL
DE |
|
|
Assignee: |
Yissum Research Development Company
Of The Hebrew University of Jerusalem Ltd.
Jerusalem
IL
QLight Nanotech Ltd.
Jerusalem
IL
Merck Patent GmbH
Darmstadt
DE
|
Family ID: |
54337845 |
Appl. No.: |
15/512944 |
Filed: |
September 20, 2015 |
PCT Filed: |
September 20, 2015 |
PCT NO: |
PCT/IL2015/050949 |
371 Date: |
March 21, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62053299 |
Sep 22, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/133723 20130101;
G02F 1/13378 20130101; G02F 2202/36 20130101; G02F 2001/13712
20130101; G02F 2001/133614 20130101; G02F 2203/01 20130101; G02F
2203/34 20130101; G02F 1/133509 20130101; G02F 1/137 20130101; G02F
2001/133742 20130101; G02F 1/133617 20130101; G02B 5/208
20130101 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; G02F 1/1337 20060101 G02F001/1337; G02F 1/1337
20060101 G02F001/1337; G02B 5/20 20060101 G02B005/20; G02F 1/1335
20060101 G02F001/1335; G02F 1/137 20060101 G02F001/137 |
Claims
1. A display system comprising an optically active structure
configured to generate patterned illumination generating desired
image, the optically active structure comprising at least one layer
comprising optically active nanorods configured to emit output
light of a predetermine wavelength range in response to pumping
energy, and liquid crystal material.
2. The display device of claim 1, wherein the display system is at
least partially transparent to visible light.
3. The display system of claim 1, wherein said at least one layer
comprises a mixture of said optically active nanorods and said
liquid crystal material such that variation in orientation of the
liquid crystal material causes corresponding variation in
orientation of said optically active nanorods.
4. The display system of claim 1, wherein said optically active
nanorods are configured to be responsive to pumping energy being
optical pumping of a first predetermined wavelength range, to
thereby emit light of one or more second wavelength ranges.
5. The display device of claim 4, wherein said first wavelength
range comprises at least one of the following: violet light and
ultra violet light wavelengths and wherein said one or more second
wavelength ranges comprise visible light.
6. The display device of claim 1, wherein said optically active
structure comprises an electrode arrangement configured to
selectively apply electric field onto said liquid crystal material
to thereby cause variation in orientation thereof.
7. The display system of claim 6, wherein said electrode
arrangement comprises plurality of electrode elements defining a
plurality of separately operated pixel regions of said optically
active structure.
8. The display device of claim 1, wherein said optically active
nanorods comprise nanorods of two or more types, each nanorods'
type is selected in accordance with dimension and structure and
composition of the nanorods to emit light of predetermined
different wavelength range.
9. The display device of claim 8, wherein said nanorods of two or
more types comprise at least three types of nanorods, each type is
selected to emit light of a predetermined wavelength range
corresponding with a primary color.
10. The display device of claim 1, wherein the display device
comprises a pumping light source configured to provide pumping
energy in the form of optical pumping of a first wavelength range
to thereby cause said optically active nanorods to emit light of
one or more second wavelength ranges.
11. The display device of claim 10, wherein said pumping light
source being configured to be located at a predetermined distance
from said optically active structure, said predetermined distance
being higher than 1 centimeter.
12. The display device of claim 1, further comprising at least one
filter layer configured to filter out light of undesired wavelength
ranges.
13. The display device of claim 12, wherein said filter layer is
configured to block transmission of ultra violet illumination and
allow transmission of light of the visible spectrum.
14. The display device of claim 1, wherein said liquid crystal
material and said optically active nanorods of the optically active
structure are mixed together such that variation in orientation of
said liquid crystal material in certain region of the structure
caused variation of rotation of said optically active in said
region, thereby increasing or reducing optical emission from said
nanorods in response to pumping energy.
15. The display device of claim 1, wherein variation of orientation
of the liquid crystal material and the corresponding nanorods
provides an OFF state where the nanorods are aligned with long axis
thereof being parallel to general direction of output light
propagation, and ON state where the nanorods are aligned with long
axis thereof being parallel to a surface of said at least one layer
and emit light in response to pumping energy.
16. The display device of claim 15, wherein the optically active
structure is further configured for providing one or more
intermediate states associated with orientation of the liquid
crystal material thereby enabling one or more intermediate levels
of optical emission from one or more pixel regions.
17. An optically active structure comprising at least one layer
comprising liquid crystal material and a plurality of optically
active nanorods mixed together within said at least one layer,
wherein in one orientation of the liquid crystal material, the
nanorods respond to input radiation of a first pumping wavelength
range by emitting light of one or more predetermined second
wavelength ranges at a first intensity level and in another
orientation of the liquid crystal material the emission from the
nanorods is reduced to a second intensity level.
18. The optically active structure of claim 17, wherein the
optically active nanorods are configured as having material
composition and geometry to emit light of said at least one second
wavelength range.
19. The optically active structure of claim 17, wherein the liquid
crystal material is configured to vary orientation thereof in
response to external electric field, and wherein variation in
orientation of the liquid crystal material causes said optically
active nanorods rotation accordingly, thereby varying emission of
light by the nanorods.
20. The optically active structure of claim 19, wherein said
variation in orientation of the liquid crystal material provides
for a continuous variation of emission of light from the
nanorods.
21. The optically active structure of claim 19, wherein the liquid
crystal material in the optically active nanorods are aligned along
a predetermined axis parallel to surface of the structure in one
orientation state and vary orientation thereof to be aligned along
a predetermined axis perpendicular to the surface of the structure
in another orientation state.
22. The optically active structure of claim 17, wherein the liquid
crystal material has a negative dielectric anisotropy.
23. The optically active structure of claim 17, further comprising
an electrode arrangement comprising a plurality of electrode
elements defining a plurality of separately operable pixels of the
structure, said electrode elements of the electrode arrangement are
configured to selectively apply electric field to corresponding
pixels to thereby cause rotation of the liquid crystal material and
optically active nanorods.
24. The optically active structure of claim 17, comprising
optically active nanorods of two or more type, wherein each type
comprises optically active nanorods having material composition and
dimensions selected to provide optical emission in selected
wavelength range different from wavelength range of nanorods of
other types.
25. The optically active structure of claim 24, wherein optically
active nanorods of different type are being arrange is a plurality
of pixel regions of the structure thereby enabling color image
formation by selective spatial and temporal variation of emitted
light.
26. The optically active structure of claim 17, wherein said
optically active structure, liquid crystal and optically active
nanorods thereof are configured to be optically partially
transparent to light of the visible spectrum, said optically active
nanorods being configured to emit light of visible spectrum in
response to pumping light in a first wavelength range comprising
ultra-violet (UV) or violet illumination.
27. The optically active structure of claim 17, wherein the liquid
crystal material comprises nematic liquid crystals material.
28. The optically active structure of claim 17, further comprising
at least one alignment layer located in physical contact with said
liquid crystal material, said at least one alignment layer is
configured to align the liquid crystal material in rest state
thereof.
29. The optically active structure of claim 28, wherein said at
least one alignment layer comprising polymer stabilized vertical
alignment layer.
30. The optically active structure of claim 17, further comprising
one or more domain separators located is physical contact with the
liquid crystal material and nanorods material at one or two sides
of the structure to thereby provide multi-domain alignment of the
liquid crystal material and the corresponding nanorods.
31. The optically active structure of claim 17, configured for use
in a display device.
32. A display device comprising: a pumping light source configured
to provide optical illumination of a first pumping wavelength
range; an optically active structure according to claim 17, and an
electrode arrangement configured to selectively apply electrical
field to desired pixel regions of the optically active structure to
thereby modulate light emission of nanorods in desired pixel
regions of the display device.
33. A display device according to claim 32, wherein the display
device is at least partially transparent to light of the visible
wavelength range.
34. The display device of claim 32, further comprising a
blocking/diffusing layer located between the device and light
arriving from back-scene thereof, the blocking/diffusing element is
configured to selectively block or diffuse light of a predetermined
wavelength range arriving from back-scene of the device.
Description
TECHNOLOGICAL FIELD
[0001] The present invention is generally in the field of optical
display systems and more specifically in the field of flat panel
display systems.
BACKGROUND
[0002] Flat panel display systems are widely used in various
devices/systems, such as computer monitors, laptop computers,
mobile phones, television sets etc. Generally, flat panel displays
became the main display type in the market.
[0003] Liquid Crystal (LC) based display systems take a major part
in the variety of flat screen display systems. The LC based display
systems utilize molecular materials combining certain liquid
properties together with crystal-like order between the molecules.
The presence of liquid properties allows varying orientation of the
LC material in response to external field, e.g. electric field.
Different orientations of the LC molecules are typically
distinguishable by having different optical properties such as
birefringence and/or transmission or rotation of polarized
light.
[0004] Generally, LC-based display systems utilize corresponding
back-illumination units providing high intensity and mostly uniform
lighting across the surface of the device. The LC panel of the
display system provides modulation to the uniform back-illumination
by completely or partially blocking light arriving from different
regions along the surface. To provide sufficient modulation, the
light illuminated by the back-illumination unit is converted to
polarized light (e.g. by an input polarizer that is attached to the
bottom part of the LC cell) while phase variation (e.g. rotation)
of the LC material varies its transmission to the polarized
light.
[0005] Various types of LC based displays are known in the art,
including devices based on LC materials with negative dielectric
anisotropy such as those described in U.S. Pat. Nos. 5,384,065 and
5,599,480.
[0006] Additionally, various types of back illumination units are
known, including units utilizing optical emission of nanoparticles,
e.g. nano-dots and rod-shaped nanoparticles. Such optical display
device and illumination units are described for example in U.S.
Pat. No. 8,471,969, and US patent publications 2013/181,234 and
2014/009,902, all assigned to the assignee of the present
application. Such nanoparticles based lighting units are capable of
providing high intensity illumination with a desired color
temperature, while reducing energy costs, and in some cases,
eliminating or at least reducing the need for polarization
filtering.
[0007] Further, several display device configurations provide
certain transparency to light arriving from back side of the
display system. Some known technologies providing at least
partially transparent display include: translucent holographic
projection systems; Transparent Organic LED (TOLED) display;
Reflective head-up display (HUD); Blue reflective thick sheet based
display; and Transparent LCD. These techniques provide display to
user while allowing transmission of light through the display to
enable user view of back side scene of the display system.
[0008] For example US 2014/0292839 provides a transparent display
device including a liquid crystal panel. The liquid crystal panel
includes a color filter substrate, an array substrate, a liquid
crystal layer, a first polarizer and a second polarizer. The first
polarizer is disposed on a side of the color filter substrate far
from the liquid crystal layer. The second polarizer is disposed on
a side of the array substrate far from the liquid crystal layer.
The color filter substrate includes a transparent base, and a color
filter formed on the transparent base. The color filter includes
compound pixel regions, wherein each of the compound pixel regions
has color sub-pixel regions and a transparent sub-pixel region. The
second polarizer includes a non-polarized pattern spatially
corresponding to the transparent sub-pixel region in the color
filter, after a light passing through the non-polarized pattern,
the polarization state remains unchanged.
General Description
[0009] As indicated above, LC-based display devices typically
utilize the variation of optical transmission to provide modulated
illumination (i.e. display an image). More specifically, the image
shown on a display device is generated by blocking, or partially
blocking, light transmission through different regions/pixels of
the device. Such transmission blocking based display techniques
require high intensity back illumination causing them to fall
behind in energy efficiency.
[0010] Additionally, the conventional configuration of transparent
or partially transparent display systems suffers from various
limitations such as limited viewing angles, low contrast and
brightness, and difficulty in scaling up in display size. The
technique of the present invention utilizes optically active
nanoparticles, and in particular nanorods and optical emission
therefrom to provide transparent display system capable of
providing desirably high brightness while maintaining transparency
of the system (e.g. transmission of 15% or more, preferably 30% and
more preferably 40% or more, of visible light passing through the
display. There is thus a need in the art for a novel configuration
of the display device. The present invention provides an optically
active layer/structure configured for use in display devices. The
optically active structure is capable of allowing the display
device to perform with increased energetic efficiency.
Additionally, the use of the optically active structure of the
invention enables design of optically transparent display systems.
The optically active structure of the invention comprises one or
more layers having a plurality of optically active rod-shaped
nanoparticles embedded within a liquid crystal (LC) molecular
matrix. The rod-shaped nanoparticles are preferably aligned with
the LC material such that orientation variation of the LC molecules
causes rotation/shifting of the nanoparticles together with the LC
molecules.
[0011] The optically active rod-shaped nanoparticles are selected
to absorb light of a predetermined first wavelength range typically
corresponding to a range between blue light and UV, and typically
including UVA range (320-400 nm) range and/or violet wavelength
range (380-450 nm), and emit in response light of one or more
second wavelength ranges (generally within the visible spectrum).
It should be noted that the wavelengths of the second wavelength
range are determined in accordance with size, geometrical shape and
material composition of the nanoparticles. Similarly, absorption of
light of the first wavelength range is typically determined in
accordance with material composition of the nanoparticles.
According to some preferred embodiments, the nanoparticles are
selected to be anisotropic nanoparticles, i.e. having one axis
longer than the others. Additionally, according to some of the
preferred embodiments, the nanoparticles are selected to be
rod-shaped semiconductor nanoparticles. Such rod-shaped
nanoparticles (also referred to as nanorods) may have core-shell,
core-double shell or core-multi-shell structure, where the core is
formed of a first material composition and the one or more shells
are formed of one or more other material compositions.
Additionally, the core itself may be a single material core, a
core-shell or core-multi-shell and may be of anisotropic geometry
or not.
[0012] Rod-shaped nanoparticles (nanorods) generally show
dipole-like optical emission in response to optical or electric
pumping energy. Additionally, nanorods typically provide optical
emission with relatively high polarization ratio (PR) of the
emitted light. To this end polarization ratio is generally defined
as a ratio between emitted intensity of light having parallel
polarization and perpendicular polarization with respect to axis of
alignment of the nanorods. More specifically, upon appropriate
pumping the nanorods emit light of a predetermined wavelength
range, determined in accordance of nanorods' parameters, and the
emitted light propagates substantially in directions perpendicular
to the long axis of the nanorods. Additionally, light emitted by
the nanorods is substantially linearly polarized, i.e. may have a
polarization ratio (PR), defined as the ratio measured between
intensity of nanorods' emissions of parallel and perpendicular
polarization with respect to the nanorods long alignment axis,
higher than 1.5, or preferably higher than 4. Thus, rotation of the
nanorods varies the direction of propagation of light emitted
therefrom, and may also vary the polarization and polarization
orientation of the emitted light.
[0013] To this end, the LC layer, in which the nanorods are
embedded, is configured to vary the orientation of the LC molecules
in response to external field. Generally, the LC layer is
configured for responding to external electric field, being direct
current (DC) or alternating current (AC) field, by varying
orientation of the LC molecules. In some embodiments, the LC
molecules are configured to be aligned parallel to the surface of
the layer in one orientation (planar orientation) and aligned
vertical to the surface of the layer in a second orientation
(vertical/homeotropic orientation). Additionally, rotation of the
LC material is preferably configured to also vary orientation of
the nanorods embedded therein. This rotation of the nanorods may
affect at least one of absorption of the pumping energy by the
nanorods and one or more properties of light emitted from the
nanorods as will be described in more details further below.
[0014] Thus, as described above, according to some embodiments, the
present invention provides a display system carrying the optically
active structure being configured and operable to response to input
pumping energy (e.g. pumping light) and provide, in accordance with
operational commands from a control unit, structured light emitted
from the device. In some embodiments, the display system is
configured to be at least partially transparent to visible light.
The display device is typically configured to vary light emitted
therefrom to generate one or more output images having
predetermined times of presentation (e.g. a video display).
[0015] Thus, according to one broad aspect the present invention
provides an optically active structure comprising at least one
layer comprising liquid crystal material and a plurality of
optically active nanorods mixed together within said at least one
layer, wherein in one orientation of the liquid crystal material,
the nanorods respond to input radiation of a first pumping
wavelength range by emitting light of one or more predetermined
second wavelength ranges at a first intensity level and in another
orientation of the liquid crystal material the emission from the
nanorods is reduced to a second intensity level.
[0016] The optically active nanorods may be selected as having
material composition and geometry to emit light of said at least
one second wavelength range.
[0017] The liquid crystal material is preferably configured to vary
orientation thereof in response to external electric field.
Further, variation in orientation of the liquid crystal material
preferably cause rotation of axis of alignment of said optically
active nanorods accordingly, thereby varying properties of light
absorbed by and emitted from the optically active nanorods. The
variation in orientation of the liquid crystal material may provide
a continuous variation of emission of light from the nanorods.
[0018] Generally, the liquid crystal material in the optically
active nanorods may be aligned along a predetermined axis parallel
to surface of the structure in one orientation state and vary
orientation thereof to be aligned along a predetermined axis
perpendicular to the surface of the structure in another
orientation state. In some embodiments, the liquid crystal material
may be configured with negative dielectric anisotropy.
[0019] The nanorod material may be selected or configured to vary
its emission properties in response to external electric field; the
applied electric field may cause quenching of the nanorod emission
of light reducing intensity of light emission in the presence of
electric fields. It should be noted however, that the nanorods'
material is preferably selected such that presence of external
electric field substantially does not significantly vary wavelength
of emission, this is to avoid color variation when emission
intensity is reduced.
[0020] The optically active structure may further comprise an
electrode arrangement comprising a plurality of electrode elements
defining a plurality of separately operable pixels of the
structure, said electrode elements of the electrode arrangement are
configured to selectively apply electric field to corresponding
pixels to thereby cause rotation of the liquid crystal material and
optically active nanorods.
[0021] The optically active structure may comprise optically active
nanorods of two or more type, wherein each type comprises optically
active nanorods having material composition and dimensions selected
to provide optical emission in selected wavelength range different
from wavelength range of nanorods of other types. The optically
active nanorods of different type may being arrange is a plurality
of pixel regions of the structure thereby enabling color image
formation by selective spatial and temporal variation of emitted
light (e.g. red green and blue pixel regions) and/or pixel regions
emitting white light of desired illumination temperature.
[0022] In some embodiments, the optically active structure, liquid
crystal and optically active nanorods thereof may be configured to
be optically partially transparent to light of the visible
spectrum. The optically active nanorods may be configured to emit
light of visible spectrum in response to pumping light in a first
wavelength range comprising ultra-violet (UV) or violet
illumination.
[0023] In some embodiments, the liquid crystal material may
comprise nematic liquid crystal material. In some embodiment, the
optically active structure may further comprise at least one
alignment layer located in physical contact with said liquid
crystal material, said at least one alignment layer is configured
to align the liquid crystal material in rest state thereof. The at
least one alignment layer may comprise polymer stabilized vertical
alignment layer.
[0024] The optically active structure may further comprise one or
more domain separators located is physical contact with the liquid
crystal material and nanorods material at one or two sides of the
structure to thereby provide multi-domain alignment of the liquid
crystal material and the corresponding nanorods.
[0025] Typically, it should be noted that the optically active
structure may be configured for use in a display device.
[0026] According to one other broad aspect, the present invention
provides a display device configured to selectively display a
desired pattern (an image), the device comprising:
[0027] a pumping light source configured to provide optical
illumination of a first pumping wavelength range,
[0028] an optically active structure comprising aligned nanorods
and LC material, the nanorods are configured to emit light of one
or more selected second wavelength ranges in response to the
pumping light, and
[0029] an electrode arrangement configured to provide an external
field to thereby locally vary the orientation of the LC material
and the nanorods, to thereby modulate light emission from the
nanorods; generally variation in the orientation of the LC is
configured to induce a corresponding variation in the orientation
of the nanorods thus selectively modulating light emission from
desired pixel regions of the display device.
[0030] The display device may be configured to be at least
partially transparent to light of the visible wavelength range, or
of a portion of the visible spectrum.
[0031] The display device may be configured to be dynamically
controlled to provide for displaying non-static images such as
movies. To this end the display device may comprise, or be
associated with, a control unit configured and operable to generate
image data corresponding to one or more images, and to operate the
electrode arrangement of the optically active structure to vary
orientation of the LC material in selected pixel regions to ON
and/or OFF modes, as well as intermediate levels in-between the OFF
and ON mode, to thereby form the desired images.
[0032] The display device may further comprise a blocking/diffusing
layer located between the device and light arriving from back-scene
thereof, the blocking/diffusing layer/element is configured to
selectively block or diffuse light of a predetermined wavelength
range arriving from back-scene of the device, for example, to block
light of the wavelength of the pumping light such as UV pumping
light minimizing the fluorescence of the active layer when used or
a part of all of the visible part of the spectrum (400-700 nm) thus
dimming back illumination of the scene behind the display and/or
providing a non-transparent display mode.
[0033] According to yet another broad aspect of the invention,
there is provided a display system comprising an optically active
structure configured to generate patterned illumination generating
desired image, the optically active structure comprising at least
one layer comprising optically active nanorods configured to emit
output light of a predetermine wavelength range in response to
pumping energy, and liquid crystal material. The display system may
be configured to be at least partially transparent to visible
light. The at least one layer may comprise a mixture of said
optically active nanorods and said liquid crystal material such
that variation in orientation of the liquid crystal material causes
corresponding variation in orientation of said optically active
nanorods.
[0034] In some embodiments, the optically active nanorods may be
configured to be responsive to pumping energy being optical pumping
of a first predetermined wavelength range, to thereby emit light of
one or more second wavelength ranges. The first wavelength range
may comprise at least one of the following: violet light and ultra
violet light wavelengths, said one or more second wavelength ranges
may comprise visible light.
[0035] The display device may comprise an electrode arrangement
associated with the optically active structure thereof and
configured to selectively apply electric field onto said liquid
crystal material to cause variation in orientation thereof. The
electrode arrangement may comprise plurality of electrode elements
defining a plurality of separately operated pixel regions of said
optically active structure.
[0036] In some embodiments, the optically active nanorods may
comprise nanorods of two or more types, each type is selected in
accordance with dimension and structure and composition of the
nanorods to emit light of predetermined different wavelength range.
The nanorods of two or more types may comprise at least three types
of nanorods, each type is selected to emit light of a predetermined
wavelength range corresponding with a primary color.
[0037] The display device may further comprise a pumping light
source configured to provide pumping energy in the form of optical
pumping of a first wavelength range to thereby cause said optically
active nanorods to emit light of one or more second wavelength
ranges. The pumping light source may be configured to be located at
a predetermined distance from said optically active structure, said
predetermined distance being higher than 1 centimeter, or higher
than 5 centimeter. In some configurations the pumping light source
may be located at a distance greater than 50cm, or greater than 1
meter, from the optically active structure of the display
device.
[0038] According to some embodiments, the display device may
further comprise at least one filter layer configured to filter out
light of undesired wavelength ranges. The filter layer may be
configured to block transmission of the pumping light (e.g. ultra
violet) illumination and allow transmission of background and/or
emitted light (e.g. the visible spectrum).
[0039] The liquid crystal material and said optically active
nanorods of the optically active structure may be mixed together
such that variation in orientation of said liquid crystal material
in certain region of the structure caused variation of rotation of
said optically active in said region, thereby increasing or
reducing optical emission from said nanorods in response to pumping
energy.
[0040] According to some embodiments, variation of orientation of
the liquid crystal material and the corresponding nanorods may
provide an OFF state where the nanorods are aligned with long axis
thereof being parallel to general direction of output light
propagation, and ON state where the nanorods are aligned with long
axis thereof being parallel to a surface of said at least one layer
and emit light in response to pumping energy. The display device
may be further configured for providing one or more intermediate
states associated with orientation of the liquid crystal material
thereby enabling one or more intermediate levels of optical
emission from one or more pixel regions.
[0041] According to some embodiments the display system may further
comprise a blocking/diffusing layer located between the device and
light arriving from back-scene thereof, the blocking/diffusing
element is configured to selectively block or diffuse light of a
predetermined wavelength range arriving from back-scene of the
device, thus providing "smart glass" capabilities of the display
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] In order to better understand the subject matter that is
disclosed herein and to exemplify how it may be carried out in
practice, embodiments will now be described, by way of non-limiting
example only, with reference to the accompanying drawings, in
which:
[0043] FIGS. 1A and 1B illustrate schematically a portion of a
display device utilizing an optically active layer including an LC
layer with embedded nanorods according to some embodiments of the
present invention in ON and OFF states respectively;
[0044] FIGS. 2A and 2B illustrate a portion of a display device
utilizing a vertically aligned LC layer with embedded nanorods
according to some embodiment of the present invention in OFF and ON
states respectively;
[0045] FIGS. 3A and 3B illustrate a portion of a display device
utilizing a vertically aligned LC layer in a multi-domain pixel
cell with embedded nanorods according to some embodiment of the
present invention in OFF and ON states respectively;
[0046] FIGS. 4A and 4B illustrate a portion of a display device
utilizing a vertically aligned LC layer in a patterned electrode
pixel cell with embedded nanorods according to some embodiment of
the present invention in OFF and ON states respectively;
[0047] FIGS. 5A and 5B schematically illustrate side (FIG. 5A) and
top (FIG. 5B) views of three adjacent pixels of the display
device;
[0048] FIG. 6 illustrates the layered structure of a transparent
display unit according to some embodiments of the invention;
and
[0049] FIG. 7 exemplifies the use of a transparent display unit
according to some embodiments of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0050] The present invention provides a display based on
fluorescence anisotropic nanomaterial inserted into or embedded in
a liquid crystal layer. The anisotropic nanomaterial may preferably
be configured to provide optical illumination with increased color
quality while mixing of anisotropic nanomaterial in the liquid
crystal provides for a simplified structure and modulation of
emission therefrom.
[0051] Reference is made to FIGS. 1A and 1B illustrating
schematically a cross section of a portion of a display device
(e.g. a pixel cell) 100 utilizing an optically active structure
(layer) 10 according to the present invention, shown in ON (FIG.
1A) and OFF (FIG. 1B) states. The optically active structure 10
includes a mixture of liquid crystal (LC) molecules 14 and
anisotropic nanomaterial particles 12 (nanorods) aligned together
along a preferred axis and configured to vary orientation in
response to applied external field. The active layer 10 of the
display device 100 may generally be enclosed between top 104 and
bottom 102 substrates, which are preferably transparent to light of
the visible spectrum, and possibly also to ultra violet
illumination, specifically, the top and bottom substrates may be
transparent to pumping light of the first wavelength range and
emitted light of the second wavelength ranges. Additionally, the
device may include one or more alignment/orientation layer 106,
e.g. formed by a layer of rubbed polyimide, two such layers are
shown in the figures. The device may also include, or be associated
with an electrode arrangement 107 configured to selectively provide
an electric field modulation promoting variation in orientation of
the LC material 14. Generally, variation in orientation of the LC
material 14 induces variation in orientation of the nanomaterial
particles 12 and thus provides modulation of the optical activity
of the device 100. In some configurations, the electrode
arrangement 107 includes transparent electrodes, e.g. ITO
(indium-tin oxide) based electrodes, to allow transmission of
optical radiation therethrough. The nanorods 12 of the optically
active layer 10 are selected and configured to response to input
pumping light 108 of a first wavelength range (e.g. blue, violet,
UV or any suitable wavelength based on the nanorods' material
composition and desired device applications) by emitting light of
one or more second wavelength ranges 110. The display device 100
may include a pumping light blocker 105 configured to block
unabsorbed components of the pumping light to prevent interference
in the displayed image. It should be noted that FIGS. 1A and 1B as
well as all the following figures are schematic and do not relate
to actual sizes of different elements. More specifically, relative
size of the LC material with respect to that of the nanorods is
generally out of scale and cannot be learned from the figures.
Nanorods material generally suitable for use according to the
present invention may be of length (long axis) of 8-500 nm, or
preferably between 10 to 160 nm and have width, or diameter, of a
few nanometers (e.g. 3 nm to 50 nm) and having an aspect ratio,
being the ratio between the length along the long axis and the
length along the short axes, higher than 1.5, and preferably higher
than 3. The LC molecules 14 are configured to rotate in response to
external electric field and rotate back when said electric field is
null. FIGS. 1A and 1B illustrate an example of the ON/OFF states of
the display device 100. In FIG. 1A the LC material 14 is in its
resting orientation, and aligned along an axis parallel to surface
of the structure 10. This configuration causes the nanorods 12 to
be aligned together with the LC molecules along a similar axis
parallel to the surface of the structure 10. At this orientation,
the nanorods 12 are aligned with their long axis perpendicular to
the direction of input pumping light 108 and perpendicular to the
desired direction of propagation of output emitted light 110. This
provides efficient absorption of the pumping light by the nanorods
12, and emission of light of the one or more second wavelength
ranges with significant portion thereof propagation in the desired
direction to project an image by the device. Thus output emitted
light 110 of the second wavelength range being emitted from the
nanorods may propagate in the desired direction from the display
device and towards the viewers as shown in FIG. 1A.
[0052] When an appropriate electric field is applied between
electrodes of the electrode arrangement 107, the molecules 14 of
the LC material rotate accordingly and cause corresponding rotation
of the nanorods 12 embedded in the layer 10. In this example, as
shown in FIG. 1B, the nanorods 12 are oriented in the OFF state
such that the long axis thereof is perpendicular to the surface of
the layer 10. In this configuration, light emitted from the
nanorods propagates substantially within the layer 10 and
substantially does not propagate out of the layer. Additionally,
the cross section for absorption of pumping light 108 in
back-illumination is greatly reduced as a result of the nanorods'
12 orientation as well as a result of the quenching effect on the
nanorods fluorescence caused by the external electric field applied
by the electrodes 107.Thus, appropriate variation of the
orientation of the LC material and the nanorods in a selected
region 30 (pixel) provides for local modulation of the optical
emission by the nanorods and enables turning a region of the
optically active layer between ON and OFF states including
intermediate states.
[0053] Generally, the nanocrystals 12 of this invention are
semiconductor elongated structures such as seeded nanorods,
nanorods or core/shell nanorods. The nanorods are inserted into a
suitable Liquid Crystal material 14 with or without additional
surface modification processes, such as attachment of surface
ligands etc. The nanorods may be aligned within the LC layer by the
LC molecules orientation. The LC molecules may be aligned by any
suitable technique such as utilizing rubbed Polyimide layer or by
photo alignment. Application of electric field to selected
electrodes of the display device induce local (e.g. within a pixel
region) rotation to the LC material together with the nanorods such
that long axis thereof is parallel or substantially parallel to the
electric field (e.g. with angular tolerance of .+-.10 degrees).
This switches a selected corresponding region of the display
between ON, OFF and intermediate states. It should be noted that
although in FIGS. 1A and 1B the ON state is described when no
electric field is applied and the OFF state is described as being
caused by application of electric field, this is selected by the
configuration of different embodiments as described herein below.
The "ON state" term refers to a state with strong emission of light
to the viewer and the "OFF state" term refers to a state with no
emission or weak emission of light in direction of the viewer. It
should also be noted that orientation of the nanorods with the long
axis being aligned vertically to the surface of the layer is shown
in FIG. 1B provides several effects that synergistically reduce and
minimize output light from the optically active layer.
[0054] First, the electric field applied on the nanorods, having a
direction parallel to the long axis of the nanorods provides
quenching of optical activity of the nanorods. The quenching
results by electron-hole separation under the electric field and is
described in details in U.S. Pat. No. 8,471,969 describing
quenching by any of DC and AC electric fields applied in the same
direction of the nanorods long axis. As described, electric field
applied on the nanorods results in significant quenching of the
emitted light. It should however be noted that the material and
configuration of the nanorods is preferably selected such as to
eliminate, or at least significantly reduce shifts in wavelength of
emission as a result of external electric field. This is to avoid
color variation resulting from image forming by the display
device.
[0055] Second, as indicated above, optical emission from nanorods
has substantially dipole-like distribution. More specifically, most
of the light is emitted in a direction normal to the long axis of
the nanorods and only very little light is emitted in the direction
of the long axis. By aligning the nanorods with the long axis
thereof directed at the viewer, only very small portion of emitted
light propagates towards the viewer. Thus most of the intensity of
the emitted light will be directed to the sides where appropriate
absorbers may be placed to prevent leakage of light.
[0056] Third, absorption of pumping light by the nanorods depends
on a corresponding cross section for absorption. In the so-called
"off configuration" shown in FIG. 1B, the nanorods are oriented
such that the long axis thereof is parallel to the direction of
propagation of pumping light. This minimizes the cross section for
absorption of pumping light and thus reduces emission from the
nanorods.
[0057] It should be noted that in some embodiments of the
invention, orientation variation of the LC material may also be
used for rotation of polarization of light emitted by the nanorods.
The device may typically include a polarization filter located
downstream of the optically active structure 10 with respect to
general direction of light propagation. Thus, when a region of the
device is in ON state, the LC material allows light emitted by the
nanorods to propagate without polarization rotation and be
transmitted by the additional polarization filter, and in the OFF
state, the LC may assist in rotating polarization of at least a
portion of the emitted light to thereby cause this portion to be
filtered out by the additional polarization filter.
[0058] Thus, variation of orientation of the nanorods, by applying
an electric field on the LC material, provides for eliminating, or
at least significantly reducing optical emission of the nanorods in
response to pumping light. However, in some configurations where
optical emission of the nanorods is not eliminated completely, the
orientation variation results in directing the emitted light to be
absorbed in suitable light absorbers located between pixel regions
to at least significantly reduce the emission in the outward
direction (to the viewers). This is while in the ON-state of the
pixel element of the device, generally there is no effect
preventing optical emission from the nanorods and the absorption
cross section is much larger compared to the OFF state, resulting
is high optical emission in response to pumping light. Thus, in the
ON-state, the nanorods are oriented parallel to the plane of the
optically active structure 10, providing high cross-section for
absorption of input pumping light to thereby cause optical emission
therefrom. The nanorods thus absorb strongly, emit their maximum
emission and the directionality of the emission is directed towards
the output direction of the display. In this state the orientation
of the nanorods is such that light emitted in directions of
adjacent pixels is configured to be minimal and light intensity in
the viewing direction may be at a maximum. Additionally, a suitable
back-reflector, which may typically be configured to transmit the
pumping light while reflecting light emitted from the nanorods, may
be used to direct greater portions of light in the preferred
direction.
[0059] In this connection it should also be noted that application
of intermediate voltages provides intermediate light intensity
output (commonly referred to as grayscale capability). More
specifically, intermediate field amplitude causes rotation of the
LC and nanorods to orientation that is between in plane and
perpendicular with respect to the optically active layer 10,
thereby resulting in emission of reduced light intensity and
especially light propagation in the desired direction towards the
viewer. This allows for generation of "gray-scale" pattern using
one type of nanorods providing a monochrome image. Additionally, in
a display utilizing a plurality of pixel elements, variation of the
intensity of light output from certain pixels may be used to
improve image quality. In such "multi-pixel" display system,
different pixel regions include nanorods of different optical
emission properties, i.e. nanorods emitting Red light in one pixel
and those emitting Green light in a neighboring pixel region. This
configuration provides the device with capability to present
colored images.
[0060] Additionally, and differently from the conventional LC-based
display systems, the technique of the present invention does not
require the use of any polarization filter for modulation of
optical emission and generation of images on the display. However,
as indicated above, in some embodiments the use of such
polarization filter may be beneficial. The modulation of light
output from the nanorods is generally achieved by varying
orientation of the nanorods reducing emission therefrom, and thus
light filtering is not specifically required. This omission of the
polarization filter may provide to better energy efficiency and
lower costs with better colors.
[0061] Also, the technique of the present invention allows for
configuring a completely transparent display device, i.e. a
see-through display device. This can be achieved by utilizing an
optically transparent electrode arrangement (e.g. ITO electrodes)
and optically transparent carrying substrates. In this
configuration, the pumping light may preferably be of UV wavelength
range arriving from the back of the display and/or from sides
thereof. This is while light of visible spectrum arriving from
objects located behind the display device is transmitted through
the device. This is exemplified in FIGS. 1A and 1B, showing
background scene ("additional") light input 109 and output 114 in
addition to pumping light 108 and emitted light 110.
[0062] As indicated above, the optically active structure 10 and
display device according to the present invention utilizes two main
materials groups to provide the desired optical activity and
modulation thereof. The optically active structure 10 generally
includes:
[0063] 1. Liquid Crystals material (LC)
[0064] 2. Anisotropic fluorescent semiconductor nanostructures
(nanorods)
[0065] It should however be noted that additional component such as
ligands and additives may be used in the optically active layer, to
enable and/or simplify insertion of the nanostructures into the
liquid crystal.
[0066] Various types of liquid crystal materials and mixtures can
be used in combinations with the nanorods. These materials are
preferably capable of aligning in a homogenous (also known as
planar) alignment. The LC material may preferably be nematic LC
material, however other types of LC material may be used. The
nematic LC material may have a dielectric negative or positive
anisotropy. Alignment of the LC is typically induced by an external
electrical field and/or by the boundary conditions of the substrate
surface that is in contact with the LC material of the optically
active layer. For example, a polyimide coating of the substrate
that is optionally rubbed can align the LC molecules parallel to
the substrate surface. Other combinations and phases of LC
materials can also be used.
[0067] Suitable LC materials are generally known in the art. The
material properties may be chosen according to the preferred mode
of alignment and switching of the optically active structure. In a
preferred mode a dielectric negative LC material may be selected.
It is preferably used in a configuration with a vertical alignment
of the LC material in relation to the substrate to thereby enable
optimizing the above described modulation of light emission from
the nanorods.
[0068] Optically active anisotropic nanoparticles (nanorods) that
are useful in various embodiments of the invention may be in
general made of semiconductor materials, for example II-VI, III-V,
or IV-VI semiconductors as well as various combinations thereof.
Such materials are also described in more detail in the
above-indicated patent publications including U.S. Pat. No.
8,471,969 and patent publications US 2014/009,902 and US
2013/115,455 assigned to the assignees of the present application.
A semiconductor material may be selected from CdS, CdSe, CdTe, ZnS,
ZnSe, ZnTe, ZnO, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP,
InSb, AlAs, AlP, AlSb, Cu.sub.2S, Cu.sub.2Se, CuInS.sub.2,
CuInSe.sub.2, Cu2(ZnSn)S.sub.4, Cu.sub.2(InGa)S.sub.4, Ti0.sub.2
alloys thereof, and various mixtures thereof. This list of
materials may refer to either the rod material (in the case of
nanorods), to the core and shell materials (in core/shell
nanorods), or to the seed and rod materials in seeded rod
structures. Seeded nanorods may have a seed (or core) located
asymmetrically within an elongated shell. The core may be typically
located at about one fourth to one half of the length on the
elongated particle, but other locations may also be possible.
Typical sizes for a seed may be between 1 to 20 nm and more
particularly between 2 to 10 nm in diameter. In addition to a first
shell, further shell layers may be included for stability and
optical function. The material combination and dimensions of the
nanorods are typically tuned to provide tuning of optical emission
is desired colors as required for the application.
[0069] The length of the overall nanorod structures may exemplarily
range between 8 nm to 500 nm and better between 10 to 160 nm. The
overall diameter of a rod may exemplarily be between 1-20 nm, and
more particularly between 1-10 nm. A typical nanorod has an aspect
ratio length/diameter of above 1.5, or preferentially above 3.
Through control of size and compositions, the emission color of the
anisotropic nanorods can be tuned for different samples to provide
the required base colors of a display. For example, a single type
of rod sample can be used for a monochromatic backlight source for
a monochrome display, or a combination of two or more different
rods emitting at different colors can be used for a color display.
As indicated above, variation in dimension, structure, and
material/chemical composition (e.g. aspect ratio, geometric shape,
different composition of core and/or various shells of the nanorods
etc.) of the nanorods are generally used to control wavelength of
emission thereof. For example, diameter variations of the seed and
rod are used to control wavelength of emission.
[0070] The nanorods are configured such that each type of nanorods
emit light having a relatively narrow bandwidth, and with a
wavelength range in the visible spectrum. Generally, the nanorods
are selected to emit light of visible colors commonly used in the
display industry (e.g. Red, Green and Blue) however additional
colors or combination of colors may be used to enhance image
quality. Typically nanorods may be selected to emit light with Full
Width Half Maximum (FWHM) below 60 nm to thereby provide high
quality colors, and in some cases below with FWHM of 45 nm or
below.
[0071] The nanorods may be covered/surrounded by molecular ligands
capable of enhancing the optical properties of the nanorods and in
some configurations, to assist in providing common rotation of the
nanorods with the LC material. The molecular ligands may also
increase dispersion of the nanorods and LC within the layer,
providing higher and uniform distribution of the nanorods within
the optically active layer. Ligand coverage of the nanorods can be
obtained at the synthesis stage of the nanorods or can be exchanged
after the nanorods are synthesized. Various ligands are used to
transfer the nanorods into aqueous or organic solutions.
[0072] Thus, to provide a pixel structure of the display device,
the optically active layer is configured with a plurality of pixel
regions, each containing LC and nanorods selected to emit light of
one or more wavelength ranges (typically each pixel is configured
to emit light of one color). Specifically, the optically active
layer may be located in between two (preferably transparent)
substrates, and include an electrode arrangement including
plurality of preferably transparent electrodes arranged along the
structure (across a surface thereof), e.g. on both or one of the
substrates, to selectively apply suitable electric field to
different pixel regions. The different electrodes of the electrode
arrangement are configured to generate localized electric fields
onto the optically active structure and thereby define and operate
pixel regions of the layer. In some configurations, at least one
substrate is coated by an orientation layer, e.g. polyimide
material, or any other material configured to by rubbing or provide
alignment of the LC material to a specific direction with respect
to the plane of the substrate. As described above, the LC material
is preferably configured to be aligned in parallel to the surface
of the optically active layer. However, as will be described
further below, additional orientations of the LC material may be
used.
[0073] Referring back to FIGS. 1A and 1B, it should be noted that
the optically active structure may preferably be configured to
allow transmission of visible light through the device 100, while
absorbing input pumping light (e.g. UV light) resulting in emission
of output light by the nanorods in the ON and intermediate states.
It should be noted that in this connection the structure may be
optically transparent to ambient light of the visible spectrum in
the meaning that at least 15%, and preferably 40% or more, of light
arriving from one side of the structure may be transmitted
therethrough. Typically the use of liquid crystal material in the
optically active structure of the invention causes rotation in
polarization of light passing therethrough, in this connection as
portion of light passing through the structure may be reflected or
absorbed in accordance with polarization states thereof. It should
further be understood that the optically active structure and a
display device utilizing the structure may or may not utilize one
or more polarizer filters for enhancing display quality. Such
polarizer filters may reduce optical transmission of ambient light
through the device.
[0074] Additionally, the exact profile of response of the optically
active structure to applied field with or without pumping energy
(e.g. pumping light) actually depends on plurality of design
parameters of the structure. These parameters include measure of
the LC-nanorod alignment response, response of the nanorod to
electric field (e.g. quenching emission due to external electric
field), mechanical properties of the optically active nanorods,
concentration of the nanorods in the LC layer and the frequency and
waveform of the applied field affecting the LC and the
nanorods.
[0075] As indicated above, according to some embodiment of the
present invention, the LC and nanorods layer may be configured to
be in ON state with zero electric field and to be turned OFF upon
application of electric field. This configuration may be provided
utilizing nematic liquid crystals. In some other embodiments, the
"on state" may be obtained upon application of electric field while
the "off" state is the rest state of the device, obtained with no
application of electric field. This may be provided using
homeotropic liquid crystal material, as commonly used in various
vertical alignment (VA) type liquid crystal based devices.
Reference is made to FIGS. 2A and 2B illustrating OFF (FIG. 2A) and
ON (FIG. 2B) states of the display device according to some
embodiments of the invention. FIG. 2A shows homeotropic LC 14 with
embedded nanorods 12. When electric field is provided by electrodes
107, a layer of the LC material rotates to be in plane with the
optically active layer thereby rotating the corresponding nanorods
and allowing emitted light to be directed out of the layer. As
shown in the figure, the layer/region of the LC material 14 may be
configured to vary orientation thereof along the entire region of
the layer 10 or such that a portion of the LC material 14 rotates
while a portion is left in rest state. This provides rotation of
the optically active nanorods 12 to enable optical emission 110
therefrom in response to pumping light 108.
[0076] FIGS. 3A and 3B illustrate multi-domain vertical alignment
(MVA) configuration of the optically active layer. This
configuration includes domain separating elements 116 extending
from the substrate to vary alignment of the LC. Generally, FIG. 3A
shows OFF stated with no electric field applied and FIG. 3B shows
the ON states when electric field is applied on the region.
Separating features (e.g. protrusions) 116 are located on one or
two sides of the LC/nanorods mixture region to produce multi-domain
alignment of the liquid crystal material 14 within region of the
structure defining a single pixel.
[0077] FIGS. 4A and 4B illustrate an additional configuration
utilizing patterned vertical alignment (PVA) layer. In this
configuration two separated electrodes 117 are located in vicinity
of a pixel region and configured to apply voltage of equal
magnitude on the top substrate part. FIG. 4A shows OFF stated with
no electric field applied and FIG. 4B shows the ON states when
electric field is applied on the region. Such configuration of the
optically active structure 100 enables the use of electrode
arrangement including patterned electrodes 117 that are located
within a single pixel and/or on a single side of the structure 100.
Additionally or alternatively, one or more of the electrode
elements may be patterned to provide selective access to specific
pixel region. This is while the other electrode element may or may
be not patterned.
[0078] It should be noted that the electrode arrangement may
include an arrangement of a plurality of electrode elements 117
configured to selectively and desirably apply electric field to
different pixel regions of the structure 100, and thus of the
display system utilizing the optical active structure to form
desired images. It should further be noted that according to some
embodiments of the invention the electrode arrangement may include
an arrangement of a plurality of electrode elements associated with
different pixel regions from one side of the optically active
structure, while a single electrode element providing ground
contact of the other side of the optically active structure. In
some other embodiments, both sides of the optically active
structure may utilize a plurality of pixel dedicated electrode
elements. Also, in some embodiments utilizing multi-domain vertical
alignment (MVA) configuration of the optically active structure
(the liquid crystal material) a single pixel may be associated with
a plurality of electrode elements varying electric field applied
onto one or more of the different domains of the pixel region.
[0079] Some additional configurations of the liquid crystal
material and control of its orientation, e.g. utilizing polymer
stabilized vertical alignment (PS-VA) layer, may be used. The
orientation of the LC material containing the nanorods may be
stabilized and optimized by addition of polymerizable additives
(e.g. reactive mesogens) layer in the active layer (e.g. in contact
with the liquid crystal material). The switching performance can be
improved thereby and alignment protrusions as shown in FIG. 3A
(element 116) may be omitted.
[0080] In some of the VA based devices the ON state may include
nanorods that are not directed vertically but are in the horizontal
direction and thus are not necessarily homogenously aligned. For
example in the MVA (FIGS. 3A and 3B) and PVA (FIGS. 4A and 4B) type
structures, different regions of the pixel may include nanorods and
liquid crystal molecules that are aligned at different angles with
respect to the horizontal projection on the substrate plane. In
addition the VA based devices may have additional electrode
patterning features and aligning features that are different from
those shown in FIGS. 1A and 1B.
[0081] The above described optically active structure 100 may be
used, according to some embodiments of the invention, as patterned
light emitting structure in a display device. To this end the
display device may typically include the optically active
structure, and an electrode arrangement configured to selectively
apply electric field to desired pixel regions of the structure.
Thus enables turning selected pixels between ON and OFF states to
thereby generate an image visible to a viewer. Typically, the
optically active structure may also be configured such that
adjacent pixel regions include nanorods emitting light of different
three or more wavelength ranges (colors). Typically, such different
colors include primary colors, e.g. red, green and blue; to thereby
provide full colored images by mixing. In some configurations the
optically active structure may include pixel regions of four or
more different colors, to thereby enable enhancement of image
quality.
[0082] In this connection reference is made to FIGS. 5A and 5B
schematically illustrating an exemplary portion of a display system
250 of the invention, the display system portion 250 includes three
pixels out of a two dimensional array of pixels of a display device
as described above. The electronic connections and control
structures described above are not specifically shown to simplify
the illustration. The pixel array 220 is formed by placing nanorods
material of selected (different) emission properties within
selected different pixel regions. Generally it should be noted that
pixel regions may be defined by effecting region of electrode
elements, i.e. by the electrode arrangement. However, in some
configurations different adjacent pixel regions may be physically
separated between them to prevent mixing of the LC and nanorods
between pixels. In the example shown in FIGS. 5A and 5B each pixel
or each row/column of pixels is configured with materials from a
different nanorods group and is separated from the pixels of
adjacent regions by separators 210. The separators 210 may be
configured to separate material of adjacent pixels regions and may
also provide blocking or absorbing of light that is emitted from
the corresponding pixel and its adjacent pixels to prevent leakage
of light between pixel regions. To this end, the material
composition of the separating regions 210 may preferably be
selected as having high absorbance and low reflectance for light of
the visible spectrum range, or at least of the wavelength ranges of
emission of the corresponding nanorods. For example, the separators
210 may be configured of resin with absorbing pigments or other
suitable materials.
[0083] Additionally, as also exemplified in FIGS. 5A and 5B, the
display system 250 may utilize an additional color filter layer
220, having an array of filter cells of different colors 221, 222,
223. The array of filter cells is typically aligned with the pixel
arrangement such the each filter cell corresponds to a pixel
region. And the pixel regions and filter cells are paired based on
color of emission of the pixel regions. The color filter 220 is
configured to assist in reducing light leakage from adjacent pixel
regions and/or leakage of ambient light.
[0084] It should be noted that some embodiments of the invention,
the display system 250 may be configured while nor requiring the
use of separators 210 between adjacent pixels. To this end, a
mixture of selected nanorods emitting at different selected
wavelength ranges may be mixed together within one or more pixel
regions, to thereby produce a combined emission of two or more
colors, typically red, green and blue. Thus generally providing
white light illumination. Operation of the electrode arrangement to
vary emission from different pixel regions affects emission of
nanorods of the different colors, and generally controls intensity
of emitted light from the corresponding pixel region. To provide
color display, i.e. having different pixels emitting in different
colors, the display system 250 may thus utilize color filter array
as exemplified by color filters cells 221, 222, 223 to filter
emission of the different pixel regions and cause different pixels
to emit light of different colors. This configuration may provide
less energy efficient display, however may not require the use of
border region structure (separators 210) and this reduce
manufacturing complexity.
[0085] It should be noted that the display system 250 according to
the present invention is not exemplified with, neither requires the
use of, any polarization filters to modulate light emission. This
is contrary to most liquid crystal based display relying of
polarization rotation property of the liquid crystal material.
Additionally, the conventional LC based display systems, and most
conventional display systems, are based on blocking of transmission
of light. This is while the display system of the invention is
based on modulation of light emission by nanorods within different
pixel regions. The emission of the display device of the present
invention is obtained optical excitation of light emitting nanorods
and causing fluorescence therefrom. Additionally modulation of the
emitted light to generate image on the display device is provided
by modulation of absorption and emission properties of the
nanorods. In part, the modulation effect is based on directionality
of dipole emitters (i.e. the nanorods), on generating an electrical
field inducing quenching of nanorods' emission and reducing
absorption of pumping light and variations of this effects for
different orientation of the nanorods. Thus, the display system of
the invention may be configured to provide higher light
transmission (transparence of the display system). The transmission
of ambient light through the display system is generally dependent
on concentration of the nanorods as well as on filling factor of
the pixel array and on the absorption of the nanorods in the
visible range.
[0086] It should however be noted that one or more polarizer
filters may still be used in the display system 250, which are not
specifically shown here. Generally one or more of the polarizer
filters may be located above the top substrate, i.e. directing the
viewers, to provide additional contrast between ON and OFF states.
The polarization filter may utilize the intrinsic polarized
emission of the nanorods and the fact that in the OFF orientation
thereof, any small emission intensity includes light components of
different polarizations. The terms "contrast" or "contrast ratio"
used in the context of the display system 250 according to the
invention do not refer to the commonly used term that measuring the
ratio between a white pixel and a black pixel in a regular LCD
device. These terms as used herein define a measure of the ratio
between fluorescence emission from a pixel region in the ON state
and in the OFF state, thus the contrast ratio actually relates to
the level of transparency of the display.
[0087] As indicated above, in the ON state the nanorods are aligned
within the optically active structure, i.e. parallel to surface of
the structure/layer and thus the emitted light therefrom is
substantially polarized along the nanorods' direction of alignment.
This is while in the OFF state, the nanorod are aligned "Standing"
on their tips, i.e. aligned parallel to general direction of light
propagation towards the viewers, perpendicular to surface of the
display system, and therefore emit light with no preferred
alignment or polarization. Thus, the use of a polarizer filter may
almost double achieve contrast ratio, since a polarizer blocks
about 50% of the unpolarized light emitted in the OFF state and
transmit most of the polarized light emitted in the ON state. It
should however be noted that light emission in the OFF state is
configured to be substantially negligible. It should be further
noted that this effect is mostly relevant in display devices
utilizing relatively homogeneous liquid crystal alignment within
pixel region. This is while typically multi domain type
configuration of pixel regions may not benefit the use of polarizer
filters.
[0088] Thus, as indicated above, the optically transparent display
system/device of the invention is capable of transmitting light of
a scene located behind the device while presenting an image on top
of the transmitted back-scene light. In this application there is
an advantage in lowering the optical absorption that occurs in the
LC stack. FIG. 6 illustrates schematically a layered structure of a
transparent display device 250 according to some embodiments of the
invention. The display device 250 may generally include a
lightguide layer 305, having low scattering and high transparency,
and configured to direct light emitted by a pumping light source
310 onto the LC stack and the optically active structure/layer 380
of the device operable by electrode arrangement 350 typically
including a plurality of electrode elements located in close
proximity with pixel regions of the optically active structure. The
LC stack may include two transparent supporting substrates 102 and
104 and the optically active LC/nanorod layer 380 located between
them. Although not shown here, it should be noted that the
lightguide may be replaced with a remote pumping light source as
the case may be. The lightguide 305 as shown in FIG. 6 illustrates
pumping light that can be provided without the need to allow open
UV lamp in the region behind the display device 250. As described
above, the display device 250 may include one or more color filters
220 placed on the LC stack and corresponding to the desired output
color (wavelength range of emitted light) of each pixel region. The
optical stack of the display device 250 as exemplified herein may
include one top polarizer 330, two polarizers (top polarizer 330
and bottom polarizer 340), one bottom polarizer 340 or it may be
configured with no polarizers at all. Different polarizers'
configurations provide corresponding different advantages and
performances for selected applications. FIG. 6 also illustrates a
mechanically or electronically modulated light blocker/diffuser, or
a "Smart Glass" layer, 385 located in the back side of the display
device 250. Smart Glass layers 385 are generally configured to
selectively transmit or block light transmission therethrough as
will be described in more details further below.
[0089] In addition, the display device 250 may include one or more
optional light recycling elements (not specifically shown) placed
at selected locations along the optical stack. These light
recycling elements may have selective wavelength transmission
properties or selective polarization properties. For example a film
that reflects the pumping light (e.g. UV light) may be placed in
various positions below the color filters 220. Such pumping light
reflector is preferably placed on the electrode side of the
optically active structure 380, and is preferably configured to
reflect light of the pumping wavelength range and transmit light of
the emitted wavelength range (e.g. visible light). Such light
recycling and reflecting elements may be configured for improving
optical emission by the nanorods and/or enabling the use of lower
material (amount of nanorods in the optically active structure 380)
while maintaining emission intensity for a given pumping source
intensity. If less material is needed the gap between the
electrodes can be smaller for the same nanorod in LC concentration
thus allowing, in some configurations, the use of higher electric
fields for the same voltage. This in turn may provide for greater
quenching of the nanorods' emission by the applied voltage
utilizing higher electric field. An additional reflective optical
element 320 may be placed below the lightguide 305, the reflective
optical element 320 is preferably configured with high reflectivity
for the pumping wavelength and high transmission for the visible
light and provide for directing more pumping light to the optically
active LC/NR layer 380.
[0090] As indication above, the display device of the invention
may, in some applications, benefit by not using any polarizers to
obtain desired performance. In this case, in the ON state of a
pixel region, the nanorods emit light and can thus produce an image
on the display. Pixel regions in their OFF state will be mostly
transparent and will not emit the fluorescence light. For this
configuration high transmittance may be achieved and omitting the
use of a polarizer may provide a gain of more than 50% in
transparency and pumping light transmission, not being blocked by
the bottom polarizer. This is while certain light intensity is
blocked or reflected in the case where one or two polarizers are
used. It may be also possible to omit the color filter layer 220
producing higher transmittance by approximately a factor of 3 (e.g.
in case of white light). In this case, different pixel regions are
configured to contain nanorods of different selected optical
emission properties corresponding to the pixel regions' desired
color of emission as described above.
[0091] For some applications there is benefit in using one or two
polarizers to obtain specific performance. In some embodiments it
is possible to use two polarizers 330 and 340 on the two sides of
the optically active structure 380 or optical stack thereof. For
example, selection of the relative directions of the polarizers, LC
rubbing direction and the birefringence properties of the LC to
provide various desired display properties. In some embodiments the
top 330 and bottom 340 polarizers may be aligned with the same
direction as the direction of the nanorod material. In such
configurations the LC material may be configured to rotate the
input polarized light by 90 degrees and thus causing the emitted
light to be blocked by the top polarizer 330. This would block the
back-scene light component (109 in FIGS. 1-4) in the ON state while
providing maximal fluorescence of the nanorod material. In the OFF
state the LC material is aligned vertically and thus do not rotate
polarization of light passing therethrough. This is while the
nanorods are also aligned vertically and substantially do not emit
light. Therefore in this configuration the OFF state provides for a
transparent pixel, and the ON provides pixel intensity and block
back-scene light.
[0092] Reference is made to FIG. 7 illustrating a transparent
display system 400 including an enclosure (e.g. showroom box,
refrigerator etc.) 410, the transparent display device of the
present invention 420, an object 430 (in this case a pair of shoes)
and a light source 440 configured to emit pumping light of UV or
Violet rays 450 to provide pumping energy to the nanorods.
Generally, the distance between the pumping light source 440 and
the optically active structure of the display device 420 may be
selected in accordance with display size, the dimension and
constitution of the enclosure and illumination profile of pumping
light source. For example, utilizing laser type pumping light
source may allow increasing the distance to very large distance.
Typically however, the distance between the pumping light source
440 and the display device 420 may be between a few centimeters to
one or two meters (e.g. 2 cm to 200 cm) thus maintaining pumping
intensity and uniform illumination. Additionally, typically the
distance between the pumping light source 440 and the display
device 420 may be increased for larger display area and decreased
for smaller display area.
[0093] Additional lighting may be included to illuminate the object
430 (not shown here). In some embodiments the pumping light 450 or
part of the pumping light may be provided by a separate transparent
backlight that uses edge illumination by LED or CCFL attached to
the waveguide such as shown for example in FIG. 6. In another
embodiment (not shown) the pumping light can be directed at the
display from the viewer's side of the display device.
[0094] In some embodiments the UV pumping light may be polarized
and directed to the display device in a preferred desired
polarization direction. If the UV polarization direction coincides
with the ON state nanorods' long axis direction, the nanorods
provide increased light absorbance as compared with the OFF state
that is not sensitive to the input polarization direction. This can
further increase the contrast ratio obtained by a factor of two.
The display device may also include an additional filter, e.g.
wavelength selective filter, being located in optical path of light
emitted by the display device and propagating towards viewers. The
additional filter may be use to block and/or diffuse passage of
light of the pumping wavelength range, e.g. UV (UVA) or violet
light while transmitting light of visible wavelength range such as
background and/or emitted light. The additional filter may be
configured for absorbing the light that is not absorbed in the
display itself. Since the pumping light has no or very little
visibility it is possible to increase the pumping so the display
can provide a luminescent image. This allows separating the
illumination of the object with visible light from that of the
display that uses the pumping light. This provides an advantage
over regular transparent displays where the same visible light is
used to enable the display and to illuminate the object and its
surrounding.
[0095] As the amount of light necessary for the display to output
may be changed in accordance with the surrounding ambient light
level, the display device of the invention may include a photo
sensor in the vicinity of the display on the viewer's side and
possibly also a photo sensor on the object side of the display.
These sensors are configured to detect light intensity in their
surrounding and transmit the light levels to a controller module
configured to modulate intensity of the pumping light and the
visible light that illuminates the object to provide optimal
lighting conditions for the display. For example, in daylight the
intensity of pumping light should be increased to match the high
intensity ambient light surrounding the viewers. This is while in
nighttime (relative darkness) the pumping light should be decreased
to adjust the brightness of the screen to that of the surrounding.
In this example the visible light directed at the object may be
increased (decreased) as well in daylight (dark).
[0096] In some embodiments the transparent display device according
to the present invention may be used together with one or more
selective light filtering elements, allowing the display device to
operate either in its transparent or non-transparent modes. More
specifically, the selective light filtering element(s) may be used
to convert the display device to a fluorescence non-transparent
display, i.e. having a "regular-mode" function thus providing
display of the image generated by different pixel regions while
preventing light from behind the device to reach the viewers. The
selective light filtering element may be a light blocking/diffusing
layer, located between the back-light input of the transparent
display device and the objects/scene located behind the display as
is shown in FIG. 6 (element 385). The blocking/diffusing layer may
block or at least strongly diffuse light coming from any object
and/or from the entire scene located behind the display device.
[0097] The use of a blocking/diffusing component allows the
fluorescent light emitted by the nanorods to form an image on the
display, while avoiding transmission of back-scene light through
the display. Additional mechanical screens or shutters may be used,
positioned either manually or by electronic control to provide the
desired blocking and/or diffusing of back-scene light. Preferably
the blocking/diffusing element is configured to reflect the pumping
light into the display to thereby provide pumping energy to the
nanorods of the display device.
[0098] Alternatively or additionally, one or more electronically
controlled transparent media may be used as selective light
filter(s), such selective transmitting layer is exemplified in FIG.
6 (element 385). The electronically controlled transparent media
may be either transparent or opaque/diffusive with regard to light
transmission therethrough. Such electronically controlled filters
are generally known as "Smart Windows".
[0099] "Smart Glass" display devices may generally be configured to
selectively allow or block transmission of back-scene light through
the device, while simultaneously and independently allow the
display device of the present invention to display desired images
on at least one surface of the device. Switching between a highly
transparent and a light blocking or light diffusing states, as well
as variation of the displayed images may be provided by a dedicated
control unit connected to the electrode arrangement as described
above as well as to the blocking/diffusing element and also
possibly to the pump and object light sources. "Smart Glass"
devices may use various physical and chemistry phenomena utilizing
technologies of devices such as: Electrophoretic devices,
Electro-wetting devices, Suspended Particle Devices (SPDs),
Electrochromic devices, Polymer dispersed liquid crystal devices
and Micro-blinds.
[0100] Additional technologies not listed above may be used to
provide similar function. The "Smart Glass" elements can provide an
opaque and or diffusive layer by electrical control of voltage,
thus allowing the conversion of the transparent display into a
regular display or a light blocking screen with a simple electrical
control. The "Smart Glass" may also be configured also reflect the
pumping light back to the NR-LC layer to increase the light
emission output.
[0101] Thus the present invention provides a display device
utilizing an optically active layer. The active layer includes LC
material and light emitting nanorods to provide desirably modulated
illumination in response to pumping light. The device may be
configured to provide a transparent display capable of providing
color image on top of transmission of background light of objects
located behind the device. Those skilled in the art will readily
appreciate that various modifications and changes can be applied to
the embodiments of the invention as hereinbefore described without
departing from its scope defined in and by the appended claims.
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